Inkjet printers eject drops of ink through an array of nozzles to effect printing on a media substrate. The nozzles are typically formed on a silicon wafer substrate using semiconductor fabrication techniques. Each nozzle is a MEMS (micro electro-mechanical systems) device driven by associated drive circuitry formed on the same silicon wafer substrate. The MEMS nozzle devices and associated drive circuitry formed on a single nozzle is commonly referred to as a printhead integrated circuit (IC).
Some inkjet printheads have a single printhead IC. These are scanning type printheads that traverse back and forth across the width of a page as the printer indexes the length of the page past the printhead. The Applicant has developed a range of pagewidth printheads that have a nozzle array as long as the printing width of the page. These printheads remain stationary in the printer as the page is fed past. This allows much higher print speeds but is more complicated in terms of controlling the operation of a much larger array of nozzles.
The pagewidth array of nozzles is made up of a series of separate printhead IC's placed end to end. Skilled workers in this field will appreciate that more printhead IC's can be fabricated on the unprocessed circular silicon wafers if each IC is short rather than long. Furthermore, localized fabrication defects can render an entire printhead IC defective. Hence there is less chance that each individual IC will be defective if they are shorter.
The nozzle array is configured into rows and columns with the rows extending the width of the page. The number of rows (that is, the height of the columns) depends on the number of colors (CMY, CMYK or CMYK/IR) and the number of nozzle rows provided for each color plane.
Firing all the nozzles in a row simultaneously would draw a large amount of current for a very short period of time. This is impractical for the drive circuitry. To avoid this, the nozzles, or groups of nozzles, can be fired in staggered intervals. However, firing adjacent nozzles simultaneously or consecutively can lead to drop misdirection. Firstly the droplet stalks (the thin column of ink connecting an ejected ink drop to the ink in the nozzle immediately prior to droplet separation) can cause micro flooding on the surface of the nozzle plate. If the micro floods can draw an ejected drop away from its intended trajectory. Secondly, the aerodynamic turbulence created by one ejected drop can influence the trajectory of a drop ejected from a neighboring nozzle. The second fired drop can be drawn into the slipstream of the first and thereby misdirected. Thirdly the fluidic cross talk between neighboring nozzles can cause drop misdirection.